The overall objective is to characterize the three types of hyperplastic lesions of the rat mammary gland (two hyperplastic alveolar nodules, one carcinogen-induced and the other spontaneous, and carcinogen-induced ductal hyperplasia) and to examine their neoplastic potential. Mammary tumors will be characterized according to hyperplasia of origin. Attempts will be made to enhance and inhibit tumorigenesis of the hyperplasias. The methodology will include mammary fat pad transplantation, organ culture, animal endocrine manipulation, and morphology, subgross and microscopic. Primary and transplantable hyperplasias will be studied in parallel.